1. Field of the Invention
The invention relates to an Internet communication system and particularly relates to a virtual private network communication system, a routing device, and a method thereof.
2. Description of Related Art
As the Internet thrives rapidly, under the framework of Internet Protocol Version 4 (IPv4), public Internet protocol addresses (Public IP addresses) are becoming insufficient for the fast growing number of network users. After the concept of private network or enterprise Intranet is proposed, private network is now extensively used by many organizations.
The Request for Comments (RFC) No. 1918 issued by the Internet Engineering Task Force (IETF) provides explanations to define the private network and the configuration of virtual IP under the private network. Basically, a host provided with a virtual IP in the private network may be connected to an external service by means of a gateway, etc.; however, the host does not have IP-level connectivity to an external network address.
When a host in a private network is to be connected to a computer host in the Internet, the connection can be achieved by the mechanism of NAT address translation. Nevertheless, when another host, to which this host in the private network is to be connected, is in another private network, a framework of virtual private network (VPN) is required between the two private networks, so as to transmit messages between the two private networks via the Internet. The virtual private network utilizes an encrypted tunneling protocol to achieve the security effects, e.g. confidentiality, transmission terminal verification, message accuracy, for private messages, such that the messages in the private networks would not be acquired by an external host/user. However, according to the current method of establishing tunneling protocol, the aforementioned has to go through complicated connection and setting. Therefore, how to establish connection between virtual private networks in a simpler way and at the same time maintain the security of the transmitted messages is an important issue in this field.